120 PHYLUM PROTOZOA THE SIMPLEST ANIMALS. 



Protozoa and Disease. The discoveries of recent years 

 have shown that the study of Protozoa is an inquiry 

 of great practical importance. Numerous Protozoa 

 representing the main divisions of the group are known 

 at some stage of their life history to be parasitic in the 

 human body or in domestic animals. Some of them 

 are associated with serious and fatal diseases. Thus, 

 Amoeba '(Entamcebd) histolytica causes an inflammation 

 of the intestinal mucous membrane and liver abscesses. 

 Several flagellates of the genus Trypanosoma are serious 



FIG. 53. Glossina palpalis^ tse-tse fly. 



parasites of the blood affecting man, horses, cattle, 

 camels, and other domestic animals in both the old 

 and new worlds. Trypanosoma gambiense (Fig. 54) is 

 the parasite causing the fatal " sleeping sickness," a human 

 disease disseminated by tse-tse fly, Glossina palpalis, in 

 Africa (Fig. 53). In the fully formed Trypanosome, the 

 flagellum is expanded into an undulating membrane 

 which extends down the edge of the cell. In this 

 membrane there are eight fine contractile threads or 

 myonemes, which are connected at the lower end with 

 a modified nucleus called the blepharoplast The so- 



